MARINE MOLLUSCA OF THE UNITED STATES. 191 
Genus AVICULA, Brug. 
Encyc. Meth., t. 177. 1792. 
1. A. ATLANTICA, Lamarck. Fig. 525. 
Anim. s. Vert., vii. 1822. 
Avicula hirundo, Say. Journ. Acad. Nat. Sci. Philad., ii. 262. 1822. 
Shell reddish-brown, with very numerous undulated wrinkles, 
which are disposed in radii and rendered more conspicuous by a 
white longitudinal line at the junction of each series of wrinkles ° 
with its contiguous one. 
North Carolina, southwards. 
Genus PINNA, Linneus. 
Syst. Nat.,-edit. x. 707. » L758. 
Animal with the mantle doubly fringed; foot elongated, grooved, 
spinning a powerful byssus attached by large triple muscles to the 
centre of each valve; adductors both large; palpi elongated; gills 
long. 
1. \P. seminupDA, Lamarck. Fig. 526. 
Anim. sans Vert., vii. 61. 1822. 
P. squamosissima, Philippi. 
Shell triangular, truncated; posterior side longitudinally ribbed, 
many scaled, scales delicate, erect; anterior side with the scales 
plentiful, minute, rather obsolete towards the umbones, with a few 
large, concentric wrinkles, dull olive. 
South Carolina, southwards, 
2. P. muRIcATA, Linneeus. Fig. 527. 
Syst. Nat., edit. xii. 1160. 1767. 
P. Carolinensis, Hanley. Proc. Zool. Soc. 225. 1858. 
Shell triangular, whitish, somewhat ventricose, obscurely ribbed, 
ribs armed with triangular, erect scales. 
South Carolina, southwards. 
Family OSTR.AIDA. 
Synopsis of Genera. 
Shell irregular, attached by the left valve; upper valve flat or concave, 
often plain; loWer valve convex, often plaited or foliaceous, and with a 
prominent beak ; ligamental cavity triangular or elongated ; hinge tooth- 
less; structure subnacreous, laminated, OstREA, Linnus, 
